IST inappropriate sinus tachycardia thread

So I just came across a good question on this website but unfortunately the discussion was closed because it's two years old. here is the link http://www.medhelp.org/posts/Heart-Disease/exercise-with-IST/show/287298
I wanted to further discuss the topics from that thread because I relate to it being diagnosed with IST recently. What is scary is that I when I first got into the gym (treadmill) at my highest intensity I performed my heart rate was 200+ and 200 is already cutting it apparently. I kept exercising for half an hour+ sometimes and now that I know that it is abnormal for my heart rate to be so high it scared me that I exercised that way for so long. Who else has IST? Do you exercise with it? What did your EP/Cardiologist say? Right now I am waiting to meet with an EP and it seems like they wont let me continue exercising until I get an EP study done, I just wish there was some other test that did the same thing except actually entering the body. I had bloodwork, ecg/ekgs, echocardiogram, stress tests already but it seems like those only give the tip of the problems answered. I also read somewhere in that discussion that ablation is less likely to be successful compared to something like svt ablation which worries me as well.